shared_buffers

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shared_buffers

Sets the amount of memory a Greenplum Database segment instance uses for shared memory
buffers. This setting must be at least 128KB and at least 16KB times max_connections.

Each Greenplum Database segment instance calculates and attempts to allocate certain
amount of shared memory based on the segment configuration. The value of
shared_buffers is significant portion of this shared memory
calculation, but is not all it. When setting shared_buffers, the values
for the operating system parameters SHMMAX or SHMALL
might also need to be adjusted.

The operating system parameter SHMMAX specifies maximum size of a single
shared memory allocation. The value of SHMMAX must be greater than this
value:

shared_buffers + other_seg_shmem

The
value of other_seg_shmem is the portion the Greenplum Database shared
memory calculation that is not accounted for by the shared_buffers value.
The other_seg_shmem value will vary based on the segment configuration.

With the default Greenplum Database parameter values, the value for
other_seg_shmem is approximately 111MB for Greenplum Database
segments and approximately 79MB for the Greenplum Database master.

The operating system parameter SHMALL specifies the maximum amount of
shared memory on the host. The value of SHMALL must be greater than this
value: